Import cbook again

jkseppan · jkseppan · commit ae1370fad8c5 · 2017-01-22T10:59:49.000+02:00
Otherwise this breaks after merging to master
diff --git a/lib/matplotlib/testing/compare.py b/lib/matplotlib/testing/compare.py
@@ -10,6 +10,7 @@
 import numpy as np
 
 import matplotlib
+from matplotlib import cbook
 from matplotlib.compat import subprocess
 from matplotlib.testing.exceptions import ImageComparisonFailure
 from matplotlib import _png
